U.S. patent number 10,355,178 [Application Number 16/043,102] was granted by the patent office on 2019-07-16 for light-emitting device and method for manufacturing the same.
This patent grant is currently assigned to NICHIA CORPORATION. The grantee listed for this patent is NICHIA CORPORATION. Invention is credited to Shuji Shioji.
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United States Patent |
10,355,178 |
Shioji |
July 16, 2019 |
Light-emitting device and method for manufacturing the same
Abstract
A light-emitting device includes a light-emitting element and a
light-transmissive member containing a phosphor, particles, and a
matrix, the phosphor and the particles being dispersed in the
matrix, the particles including at least one of surface-treated
particles, particles coexisting with a dispersing agent, and
surface-treated particles coexisting with a dispersing agent, the
particles being dispersed as aggregates, the particles having an
average particle diameter in a range of 1 nm to 8 nm, a content of
the particles falling within a range of 0.01 parts by mass to less
than 5 parts by mass relative to 100 parts by mass of the matrix, a
content of the phosphor falling within a range of 100 parts by mass
to 300 parts by mass relative to 100 parts by mass of the
matrix.
Inventors: |
Shioji; Shuji (Komatsushima,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NICHIA CORPORATION |
Anan-shi, Tokushima |
N/A |
JP |
|
|
Assignee: |
NICHIA CORPORATION (Anan-shi,
JP)
|
Family
ID: |
65023468 |
Appl.
No.: |
16/043,102 |
Filed: |
July 23, 2018 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20190027657 A1 |
Jan 24, 2019 |
|
Foreign Application Priority Data
|
|
|
|
|
Jul 24, 2017 [JP] |
|
|
2017-143072 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
33/504 (20130101); H01L 33/36 (20130101); H01L
33/501 (20130101); F21V 19/001 (20130101); H01L
33/62 (20130101); H01L 2933/0041 (20130101); H01L
2933/0091 (20130101) |
Current International
Class: |
H01L
33/50 (20100101); H01L 33/56 (20100101); H01L
33/62 (20100101); F21V 19/00 (20060101); H01L
33/36 (20100101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2010251621 |
|
Nov 2010 |
|
JP |
|
2011222718 |
|
Nov 2011 |
|
JP |
|
2014031436 |
|
Feb 2014 |
|
JP |
|
2015109354 |
|
Jun 2015 |
|
JP |
|
2016082212 |
|
May 2016 |
|
JP |
|
Primary Examiner: Taylor; Earl N
Attorney, Agent or Firm: Hunton Andrews Kurth LLP
Claims
The invention claimed is:
1. A light-emitting device comprising: a light-emitting element;
and a light-transmissive member covering the light-emitting
element, the light-transmissive member comprising: a phosphor;
particles; and a matrix, wherein the phosphor and the particles are
dispersed in the matrix, wherein the particles comprise at least
one of surface-treated particles, particles coexisting with a
dispersing agent, and surface-treated particles coexisting with a
dispersing agent, wherein the particles are dispersed as
aggregates, wherein the particles have an average particle diameter
in a range of 1 nm to 8 nm, wherein a content of the particles
falls within a range of 0.01 parts by mass to less than 5 parts by
mass relative to 100 parts by mass of the matrix, and wherein a
content of the phosphor falls within a range of 100 parts by mass
to 300 parts by mass relative to 100 parts by mass of the
matrix.
2. The light-emitting device according to claim 1, wherein the
particles comprise zirconium oxide.
3. The light-emitting device according to claim 1, wherein the
phosphor comprises manganese-activated barium magnesium aluminate
and manganese-activated potassium fluorosilicate.
4. The light-emitting device according to claim 1, wherein the
matrix comprises a silicone resin, a modified silicone resin, or a
hybrid silicone resin.
5. The light-emitting device according to claim 1, wherein the
light-emitting element has an emission peak in a range of 400 nm to
480 nm, and wherein the aggregates have an average particle
diameter of 10 nm to 80 nm.
6. A method for manufacturing a light-emitting device, the method
comprising: mounting a light-emitting element in a depressed
portion of a substrate; and forming a light-transmissive member in
the depressed portion to cover the light-emitting element, the
light-transmissive member comprising: a phosphor; at least one of
surface-treated particles, particles coexisting with a dispersing
agent, and surface-treated particles coexisting with a dispersing
agent; and a matrix, wherein the phosphor and the particles are
dispersed in the matrix, wherein the particles are dispersed as
aggregates, wherein the particles have an average particle diameter
in a range of 1 nm to 8 nm, wherein a content of the particles
falls within a range of 0.01 parts by mass to less than 5 parts by
mass relative to 100 parts by mass of the matrix, and wherein a
content of the phosphor falls within a range of 100 parts by mass
to 300 parts by mass relative to 100 parts by mass of the matrix in
the forming of the light-transmissive member.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. .sctn. 119
to Japanese Patent Application No. 2017-143072, filed Jul. 24,
2017, the contents of which are hereby incorporated by reference in
their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The disclosure of the present invention relates to a light-emitting
device and a method for manufacturing the same.
2. Description of Related Art
Light-emitting devices manufactured by disposing light-emitting
elements in depressed portions of packages, connecting the
light-emitting elements to lead frames with wires, and charging and
curing encapsulating resins are conventionally known (for example,
see Japanese Unexamined Patent Application Publication No.
2011-222718).
SUMMARY OF THE INVENTION
A light-emitting device according to an embodiment of the present
disclosure includes a light-emitting element and a
light-transmissive member covering the light-emitting element, the
light-transmissive member containing a phosphor, particles, and a
matrix, the phosphor and the particles being dispersed in the
matrix, the particles including at least one of surface-treated
particles, particles coexisting with a dispersing agent, and
surface-treated particles coexisting with a dispersing agent, the
particles being dispersed as aggregates, the particles having an
average particle diameter in a range of 1 nm to 8 nm, a content of
the particles falling within a range of 0.01 parts by mass to less
than 5 parts by mass relative to 100 parts by mass of the matrix, a
content of the phosphor falling within a range of 100 parts by mass
to 300 parts by mass relative to 100 parts by mass of the
matrix.
A method for manufacturing a light-emitting device according to an
embodiment of the present disclosure includes mounting a
light-emitting element in a depressed portion of a substrate and
forming a light-transmissive member in the depressed portion to
cover the light-emitting element, the light-transmissive member
containing a phosphor; at least one of surface-treated particles,
particles coexisting with a dispersing agent, and surface-treated
particles coexisting with a dispersing agent; and a matrix, the
phosphor and the particles being dispersed in the matrix, the
particles being dispersed as aggregates, the particles having an
average particle diameter in a range of 1 nm to 8 nm, a content of
the particles falling within a range of 0.01 parts by mass to less
than 5 parts by mass relative to 100 parts by mass of the matrix, a
content of the phosphor falling within a range of 100 parts by mass
to 300 parts by mass relative to 100 parts by mass of the matrix in
the forming of the light-transmissive member.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of embodiments of the invention and
many of the attendant advantages thereof will be readily obtained
by reference to the following detailed description when considered
in connection with the accompanying drawings.
FIG. 1 is a schematic top view of a light-emitting device according
to a present embodiment.
FIG. 2 is a schematic cross-sectional view taken along the line
II-II in FIG. 1.
FIG. 3 is a diagram schematically illustrating how a phosphor and
aggregated particles exist in a light-transmissive member according
to the present embodiment.
FIG. 4 is a graph showing the relation between the luminous flux
ratio and the average particle diameter and content of zirconium
oxide particles of the light-emitting device according to the
present embodiment.
DETAILED DESCRIPTION OF EMBODIMENTS
Although the present disclosure has been described with reference
to several exemplary embodiments, it shall be understood that the
words that have been used are words of description and
illustration, rather than words of limitation. Changes may be made
within the purview of the appended claims, as presently stated and
as amended, without departing from the scope and spirit of the
disclosure in its aspects. Although the disclosure has been
described with reference to particular examples, means, and
embodiments, the disclosure may be not intended to be limited to
the particulars disclosed; rather the disclosure extends to all
functionally equivalent structures, methods, and uses such as are
within the scope of the appended claims.
One or more examples or embodiments of the disclosure may be
referred to herein, individually and/or collectively, by the term
"disclosure" merely for convenience and without intending to
voluntarily limit the scope of this application to any particular
disclosure or inventive concept. Moreover, although specific
examples and embodiments have been illustrated and described
herein, it should be appreciated that any subsequent arrangement
designed to achieve the same or similar purpose may be substituted
for the specific examples or embodiments shown. This disclosure may
be intended to cover any and all subsequent adaptations or
variations of various examples and embodiments. Combinations of the
above examples and embodiments, and other examples and embodiments
not specifically described herein, will be apparent to those of
skill in the art upon reviewing the description.
In addition, in the foregoing Detailed Description, various
features may be grouped together or described in a single
embodiment for the purpose of streamlining the disclosure. This
disclosure may be not to be interpreted as reflecting an intention
that the claimed embodiments require more features than are
expressly recited in each claim. Rather, as the following claims
reflect, inventive subject matter may be directed to less than all
of the features of any of the disclosed embodiments. Thus, the
following claims are incorporated into the Detailed Description,
with each claim standing on its own as defining separately claimed
subject matter.
The above disclosed subject matter shall be considered
illustrative, and not restrictive, and the appended claims are
intended to cover all such modifications, enhancements, and other
embodiments which fall within the true spirit and scope of the
present disclosure. Thus, to the maximum extent allowed by law, the
scope of the present disclosure may be determined by the broadest
permissible interpretation of the following claims and their
equivalents, and shall not be restricted or limited by the
foregoing detailed description.
FIG. 1 is a schematic top view of a light-emitting device according
to the present embodiment. FIG. 2 is a schematic cross-sectional
view taken along the line II-II in FIG. 1. FIG. 3 is a diagram
schematically illustrating how a phosphor and aggregated particles
exist in a light-transmissive member according to the present
embodiment.
As shown in FIG. 1 and FIG. 2, a light-emitting device 100 includes
a light-emitting element 20 and a light-transmissive member 30. The
light-emitting device 100 is, for example, a surface-mount
light-emitting diode (LED) and includes a substrate 10 having a
depressed portion 15, the light-emitting element 20 accommodated in
the depressed portion 15, and the light-transmissive member 30
formed in the depressed portion 15 to cover the light-emitting
element 20. The following describes the components of the
light-emitting device according to the present invention.
Substrate 10
The substrate 10 is a member serving as a housing or pedestal in
which the light-emitting element 20 is mounted. The substrate 10
includes, as main components, electrically-conductive members 13
electrically connected to the light-emitting element 20 and a
formed body 14 supporting the electrically-conductive members 13.
The substrate 10 may be in the form of a package or a circuit
board. Specific examples of the substrate 10 include a resin formed
body integrated with a lead frame by transfer molding or injection
molding as well as a sintered product of layered ceramic green
sheets on which an electrically-conductive paste has been printed.
It is preferable that the periphery of the upper surface of the
substrate 10 be substantially flat, but the periphery may be
curved. The depressed portion 15 is formed at the center of the
upper surface of the substrate 10. The depressed portion 15 may be
formed by causing the formed body 14 itself to cave in or by
separately forming a frame-shaped protrusion on the upper surface
of a substantially flat formed body 14 so that the inside of the
projection serves as the depressed portion 15. Examples of the
shape of the depressed portion 15 in a top view include circles,
ellipses, rectangles, and rectangles with rounded corners. The
lateral walls of the depressed portion 15 are preferably inclined
such that the diameter of the depressed portion 15 increases from
the bottom surface toward the upper side of the depressed portion
15 in order to help the formed body 14 release from a mold and to
efficiently extract light from the light-emitting element 20. The
inclination includes a curve. The inclination angle of a lateral
wall of the depressed portion 15 is, for example, in the range of
95.degree. to 120.degree. from the bottom surface of the depressed
portion 15. The depth of the depressed portion 15 is not
particularly limited but is, for example, in the range of 0.05 mm
to 2 mm, preferably 0.1 mm to 1 mm, more preferably 0.25 mm to 0.5
mm.
Electrically-Conductive Members 13
The electrically-conductive members 13 are part of a lead frame
formed of a metal member that is connected to the light-emitting
element 20 and can conduct electricity. Specific examples include a
pair of positive and negative lead electrodes and wiring formed of
gold, silver, copper, iron, aluminum, tungsten, cobalt, molybdenum,
chromium, titanium, nickel, palladium, an alloy of these materials,
phosphor bronze, or a copper-iron alloy. Plating or a
light-reflective film made of silver, aluminum, rhodium, gold,
copper, or an alloy of these materials may be disposed on the outer
layer of the electrically-conductive members 13. Among these
materials, silver, which has the best light-reflecting property, is
preferable. The electrically-conductive members 13 are exposed on
the back surface of the substrate 10 and also function as heat
dissipating members.
Formed Body 14
The formed body 14 is electrically insulative and supports the
electrically-conductive members 13. Examples of the matrix of the
formed body 14 include thermoplastic resins such as alicyclic
polyamide resins, semi-aromatic polyamide resins, poly ethylene
terephthalate, poly cyclohexane terephthalate, liquid crystal
polymers, polycarbonate resins, syndiotactic polystyrene,
polyphenylene ethers, polyphenylene sulfide, polyether sulfone
resins, polyether-ketone resins, and polyarylate resins, and
thermosetting resins such as polybismaleimide-triazine resins,
epoxy resins, modified epoxy resins, silicone resins, modified
silicone resins, polyimide resins, and polyurethane resins. Such a
matrix can be mixed with, as a filler or color pigment, particles
or fibers of glass, silica, titanium oxide, magnesium oxide,
magnesium carbonate, magnesium hydroxide, calcium carbonate,
calcium hydroxide, calcium silicate, magnesium silicate,
wollastonite, mica, zinc oxide, barium titanate, potassium
titanate, aluminum borate, aluminum oxide, zinc oxide, silicon
carbide, antimony oxide, zinc stannate, zinc borate, iron oxide,
chromium oxide, manganese oxide, or carbon black. In addition, the
formed body 14 may be formed of a ceramic containing aluminum
oxide, aluminum nitride, or a mixture of these materials.
Light-Emitting Element 20
A semiconductor light-emitting element such as light-emitting diode
(LED) elements can be used for the light-emitting element 20. The
light-emitting element 20 is bonded to the bottom surface of the
depressed portion 15 of the substrate 10 with an adhesive 19 and is
electrically connected to the electrically-conductive members 13
with wires 18. The light-emitting element 20 is only required to
include an element structure made of any of various semiconductors
provided with a pair of positive and negative electrodes. In
particular, the light-emitting element 20 preferably includes a
nitride semiconductor (In.sub.xAl.sub.yGa.sub.1-x-yN, 0.ltoreq.x,
0.ltoreq.y, x+y.ltoreq.1) that can efficiently excite a phosphor
50. The light-emitting element 20 preferably has an emission peak
in the range of 400 nm to 480 nm. Alternatively, a gallium-arsenide
or gallium-phosphide semiconductor light-emitting element may be
employed. One or a plurality of light-emitting elements 20 may be
mounted on one light-emitting device 100. A plurality of
light-emitting elements 20 can be connected in series or in
parallel.
Wires 18
The wires 18 electrically connect the electrodes of the
light-emitting element 20 to the electrically-conductive members
13. Metal wires made of gold, copper, silver, platinum, aluminum,
or an alloy of these metals can be used for the wires 18. Gold
wires, which are less apt to be broken by stress generated by the
light-transmissive member 30 and have good thermal resistance and
the like, are particularly preferable for the wires 18. To enhance
the light extraction efficiency, silver may constitute at least the
surface of the wires 18.
Adhesive 19
The adhesive 19 is a member for fixing the light-emitting element
20 to the substrate 10 and is made of an insulating adhesive or an
electrically-conductive adhesive. Examples of the insulating
adhesive include epoxy resins, silicone resins, polyimide resins,
and modified or hybrid resins of these resins. Examples of the
electrically-conductive adhesive include electrically-conductive
pastes of silver, gold, and palladium; solder such as gold tin; and
brazing filler metals such as low-melting-point metals.
Light-Transmissive Member 30
As shown in FIG. 2 and FIG. 3, the light-transmissive member 30 may
cover the light-emitting element 20 disposed in the depressed
portion 15. The light-transmissive member 30 contains the phosphor
50, particles 40, and a matrix 31. The phosphor 50 and the
particles 40 are dispersed in the matrix 31.
Matrix 31
The matrix 31 preferably contains an electrically insulating
material that can transmit light emitted from the light-emitting
element 20 (preferably at a transmittance of 70% or more) and is
fluid before being hardened by heat. Specific examples of the
material constituting the matrix 31 include silicone resins, epoxy
resins, phenolic resins, polycarbonate resins, acrylic resins,
polymethyl pentene resins, polynorbornene resins, and modified or
hybrid resins of these resins. Among these resins, silicone resins,
modified silicone resins, and hybrid silicone resins have good heat
and light resistance and low volume shrinkage when being cured and
are thus preferable. The light-transmissive member 30 preferably
contains a filler and the like mixed in the matrix 31 but may not
contain the filler.
A diffusing agent or a colorant can be used as the filler. Specific
examples of the filler include silica, titanium oxide, magnesium
oxide, magnesium carbonate, magnesium hydroxide, calcium carbonate,
calcium hydroxide, calcium silicate, zinc oxide, barium titanate,
aluminum oxide, iron oxide, chromium oxide, manganese oxide, glass,
and carbon black. Examples of the shape of the filler include
spherical shapes, indefinite crushed shapes, acicular shapes,
columnar shapes, plate-like shapes (including scaly shapes),
fibrous shapes, and arborescent shapes. A hollow or porous filler
may also be used.
Phosphor 50
A predetermined amount of the phosphor 50 is mixed in the matrix 31
of the light-transmissive member 30. The phosphor 50 absorbs at
least part of primary light emitted from the light-emitting element
20 and emits secondary light that differs in wavelengths from the
primary light. Specific examples of the phosphor 50 include
manganese-activated barium magnesium aluminate (BAM:Mn phosphors),
manganese-activated potassium fluorosilicate (KSF:Mn phosphors),
europium-activated nitrogen-containing calcium aluminosilicate
(such as CASN:Eu phosphors and SCASN:Eu phosphors), and
europium-activated SiAlONs. This structure provides a
light-emitting device 100 that emits mixed light (such as white
light) of the primary light and the secondary light both having
visible wavelengths.
The content of the phosphor 50 in the light-transmissive member 30
is in the range of 100 parts by mass to 300 parts by mass relative
to 100 parts by mass of the matrix. If the content of the phosphor
50 falls within the above range, the particles 40 dispersed in the
matrix 31 are prevented from aggregating to a diameter larger than
the particle diameter that causes strongest Rayleigh scattering.
Decrease in the light transmittance of the light-transmissive
member 30 can also be suppressed. Accordingly, scattering inside
the matrix 31 of the primary light emitted from the light-emitting
element 20 is enhanced. The light extraction efficiency of the
light-emitting device 100 is thus enhanced. In the case where two
or more types of phosphors 50, such as a BAM:Mn phosphor 51 and a
KSF:Mn phosphor 52, are used, the content of the phosphor 50 is the
total content of the two or more types of phosphors 50.
If the content of the phosphor 50 is less than 100 parts by mass,
the amount of the phosphor 50 dispersed in the matrix 31 is small,
and the particles 40 dispersed in the matrix 31 aggregate to form
aggregates 41 having diameters larger than a quarter of the
wavelength of the primary light emitted from the light-emitting
element 20. Consequently, the effects of Rayleigh scattering from
the aggregates 41 are lessened, and improvement in the light
extraction efficiency of the light-emitting device 100 cannot be
expected. If the content of the phosphor 50 exceeds 300 parts by
mass, a large amount of the phosphor 50 dispersed in the matrix 31
blocks the primary light emitted from the light-emitting element 20
and reduces the light transmittance of the light-transmissive
member 30. Consequently, improvement in the light extraction
efficiency of the light-emitting device 100 cannot be expected.
The average particle diameter of the phosphor 50 is preferably in
the range of 1 .mu.m to 50 .mu.m. If the average particle diameter
of the phosphor 50 falls within the above range, aggregation of the
particles 40 dispersed in the matrix 31 and decrease in the light
transmittance of the light-transmissive member 30 are suppressed,
so that the light extraction efficiency of the light-emitting
device 100 is improved.
If the average particle diameter of the phosphor 50 is less than 1
.mu.m, the area occupied by the phosphor 50 in the matrix 31 is
small, and the particles 40 dispersed in the matrix 31 tend to
aggregate to form the aggregates 41 having diameters larger than a
quarter of the wavelength of the primary light emitted from the
light-emitting element 20. Consequently, the effects of Rayleigh
scattering from the aggregates 41 are lessened, and improvement in
the light extraction efficiency of the light-emitting device 100
cannot be expected. If the average particle diameter of the
phosphor 50 exceeds 50 .mu.m, the area occupied by the phosphor 50
in the matrix 31 is large, and the primary light emitted from the
light-emitting element 20 is blocked, so that the light
transmittance of the light-transmissive member 30 decreases.
Consequently, improvement in the light extraction efficiency of the
light-emitting device 100 cannot be expected.
The average particle diameter of the phosphor 50 can be measured by
a method such as the laser diffraction/scattering method, image
analysis (with a scanning electron microscope (SEM) or a
transmission electron microscope (TEM)), dynamic light scattering,
and small-angle X-ray scattering. The average value of the particle
diameters of a plurality of particles of the phosphor 50 measured
by the above method is regarded as the average particle diameter of
the phosphor 50. The shape of the phosphor 50 is not particularly
limited, and examples of the shapes include spherical shapes,
indefinite crushed shapes, acicular shapes, columnar shapes,
plate-like shapes (including scaly shapes), fibrous shapes, and
arborescent shapes. The maximum particle diameter measured by the
above method is regarded as the particle diameter of the phosphor
50 in the case where the phosphor 50 has a shape, such as
indefinite crushed shapes and acicular shapes, other than spherical
shapes.
Alternatively, the median diameter may be used instead of the
average particle diameter. A median diameter is a value calculated
from a mass-based or volume-based particle size distribution curve
obtained by measurement of particle size distribution by, for
example, the laser diffraction/scattering method. Specifically, the
median diameter is calculated as the particle diameter at a
cumulative mass or a cumulative volume of 50% from the
small-diameter side of the particle size distribution.
Particles 40
As shown in FIG. 2 and FIG. 3, the particles 40 scatter, inside the
matrix 31, the primary light emitted from the light-emitting
element 20. A predetermined amount of the particles 40 having an
average particle diameter in a predetermined range is contained in
the light-transmissive member 30. The particles 40 have an average
particle diameter in the range of 1 nm to 8 nm and are at least one
of surface-treated particles 40, particles 40 coexisting with a
dispersing agent, and surface-treated particles 40 coexisting with
a dispersing agent. The particles 40 are dispersed in the matrix 31
of the light-transmissive member 30 in the form of the aggregates
41 formed by aggregation of the particles 40. The content of the
particles 40 in the light-transmissive member 30 is in the range of
0.01 parts by mass to less than 5 parts by mass relative to 100
parts by mass of the matrix.
If the average particle diameter and content of the particles 40
are as described above and if the particles 40 are at least one of
the surface-treated particles 40, the particles 40 coexisting with
a dispersing agent, and the surface-treated particles 40 coexisting
with a dispersing agent, unlimited aggregation of the particles 40
is prevented, and the average particle diameter of the aggregates
41 becomes about one-tenth, at which Rayleigh scattering is
strongest, of the wavelength of the primary light emitted from the
light-emitting element 20 almost without exceeding a quarter of the
wavelength. Specifically, the average particle diameter of the
aggregates 41 is preferably in the range of 10 nm to 80 nm. If the
aggregates 41 has an average particle diameter of about one-tenth
of the wavelength of the primary light emitted from the
light-emitting element 20, Rayleigh scattering from the aggregates
41 increases the amount of scattered primary light of the
light-emitting element 20, thereby improving the light extraction
efficiency of the light-emitting device 100. Also, Rayleigh
scattering leads to excitation of the phosphor 50 and ensures
sufficient secondary light emitted from the phosphor 50.
Accordingly, the content of the phosphor 50 in the
light-transmissive member 30 can be reduced compared with
conventional contents, so that the light transmittance of the
light-transmissive member 30 is improved. The light extraction
efficiency of the light-emitting device 100 is thus enhanced, and
the cost of the light-emitting device 100 can be reduced.
If the particles 40 have an average particle diameter less than 1
nm, which is too small, the aggregates 41 formed by aggregation of
the particles 40 have an average particle diameter less than 10 nm.
Rayleigh scattering from the aggregates 41 is thus reduced, and
increase in the amount of scattered primary light of the
light-emitting element 20 cannot be expected. If the particles 40
have an average particle diameter larger than 8 nm, which is too
large, the aggregates 41 formed by aggregation of the particles 40
have an average particle diameter larger than 80 nm. The aggregates
41 thus block the primary light emitted from the light-emitting
element 20, and increase in the amount of scattered primary light
of the light-emitting element 20 cannot be expected.
The aggregates 41 are larger than the particles 40 and are easily
observed. Hence, the existence of the particles 40 can be inferred
from observation of the existence of the aggregates 41. The average
particle diameter of the particles 40 or the aggregates 41 can be
measured by a method such as the laser diffraction/scattering
method, image analysis (with a scanning electron microscope (SEM)
or a transmission electron microscope (TEM)), dynamic light
scattering, and small-angle X-ray scattering. The average value of
the particle diameters of a plurality of particles 40 or aggregates
41 measured by the above method is regarded as the average particle
diameter of the particles 40 or the aggregates 41. Alternatively,
the median diameter described above may be used instead of the
average particle diameter.
The shape of the particles 40 or the aggregates 41 is not
particularly limited and may be an indefinite crushed shape, but a
spherical shape is preferable because such a shape minimizes
contact between the particles 40 or between the aggregates 41 and
suppresses aggregation. Also, plate-shaped particles 40 or
aggregates 41 can impart gas barrier properties to the
light-transmissive member 30. The maximum particle diameters
measured by the above method are regarded as the particle diameters
of the particles 40 or the aggregates 41 in the case where the
particles 40 or the aggregates 41 have a shape, such as indefinite
crushed shapes and plate-like shapes, other than spherical
shapes.
If the content of the particles 40 is less than 0.01 parts by mass,
only a small amount of the particles 40 aggregates, and many of the
aggregates 41 formed by aggregation of the particles 40 have a size
less than 10 nm. Rayleigh scattering from the aggregates 41 is thus
reduced, and increase in the amount of scattered primary light of
the light-emitting element 20 cannot be expected. If the content of
the particles 40 is 5 parts by mass or more, a large amount of the
particles 40 aggregates, and many of the aggregates 41 formed by
aggregation of the particles 40 have sizes larger than 80 nm. The
aggregates 41 thus block the primary light emitted from the
light-emitting element 20, and increase in the amount of scattered
primary light of the light-emitting element 20 cannot be
expected.
The material for the particles 40 is not particularly limited and
may be an organic or inorganic substance. A light-transmissive
substance is preferably used for the particles 40 in view of the
light extraction efficiency of the light-emitting device. The
particles 40 preferably have a melting point of 260.degree. C. or
higher in view of solder heat resistance.
Specific preferable examples of the organic substance used for the
particles 40 include resins such as polymethacrylate esters and
their copolymers, polyacrylate esters and their copolymers,
cross-linked polymethacrylate esters, cross-linked polyacrylate
esters, polystyrene and its copolymers, cross-linked polystyrene,
epoxy resins, silicone resins, and amorphous fluorocarbon resins.
Core-shell particles 40 produced by coating inorganic particles
with at least one selected from the above resins are also included.
Since the refractive index of such organic particles 40 can be
adjusted to the refractive index of the matrix 31 of the
light-transmissive member by copolymerization, the particles 40
have little optical effect. For example, the particles 40 maintain
the light-transmissive property.
Preferable examples of the inorganic substance used for the
particles 40 include oxides such as silicon oxide, aluminum oxide,
zirconium oxide, titanium oxide, zinc oxide, magnesium oxide,
gallium oxide, tantalum oxide, niobium oxide, bismuth oxide,
yttrium oxide, iridium oxide, indium oxide, and tin oxide. Such
inorganic particles 40 have good heat and light resistance and have
comparatively high thermal conductivity. Among these substances,
silicon oxide, aluminum oxide, zirconium oxide, and titanium oxide
are easily available and comparatively inexpensive.
The particles 40 are at least one of the surface-treated particles
40, the particles 40 coexisting with a dispersing agent, and the
surface-treated particles 40 coexisting with a dispersing agent.
The surface treatment of the particles 40 is performed by
chemically bonding a surface treatment agent to the surface of the
particles 40. Examples of the surface treatment agent include
long-chain aliphatic amines and their derivatives; long-chain
aliphatic fatty acids and their derivatives; silane couplers;
siloxane compounds containing the amine group and/or the carboxy
group; siloxane compounds containing at least one selected from the
silanol group, the hydrogen silane group, and the alcohol group;
siloxane compounds containing the vinylsilyl group and at least one
selected from the silanol group, the alkoxy group, and the hydrogen
silane group; monoglycidyl ether terminated siloxane compounds;
monohydroxy ether terminated siloxane compounds; organic silazane
compounds; organic titanate compounds; isocyanate compounds; epoxy
compounds; and phosphate compounds.
Examples of the dispersing agent coexisting with the particles 40
or the surface-treated particles 40 include, in addition to the
above surface treatment agents, macromolecular compounds containing
an acidic or basic group, fluorine-containing surfactants, polyol
compounds, polyethylene oxide derivatives, polypropylene oxide
derivatives, polyunsaturated fatty acid derivatives, silane coupler
hydrolysates, and quaternary ammonium salt compounds. As described
later in the section on a method for manufacturing the
light-emitting device, the particles 40 coexisting with a
dispersing agent are obtained by adding the dispersing agent to a
slurry containing the phosphor 50, the particles 40, and the matrix
31, and examples thereof include particles 40 that have adsorbed
the dispersing agent.
The method for manufacturing the light-emitting device includes
mounting a light-emitting element and forming a light-transmissive
member. The following describes each step. The structure of the
light-emitting device is described referring to FIG. 1 to FIG.
3.
Mounting Light-Emitting Element
In the mounting of the light-emitting element, the light-emitting
element 20 is mounted in the depressed portion 15 of the substrate
10. First, the substrate 10 and the light-emitting element 20 are
provided by conventionally known manufacturing methods.
Subsequently, the light-emitting element 20 is mounted in the
depressed portion 15 as described below.
In the case of a light-emitting element 20 having a pair of
positive and negative electrodes on the same surface, the
light-emitting element 20 is face-up mounted in the depressed
portion 15 of the substrate 10 such that the pair of positive and
negative electrodes on the upper surface are connected to the
electrically-conductive members 13 with the wires 18 as shown in
FIG. 1 and FIG. 2, or the light-emitting element 20 is face-down
(flip-chip) mounted in the depressed portion 15 of the substrate 10
such that a pair of positive and negative electrodes, which are not
shown, on the lower surface are connected to the
electrically-conductive members 13 via the adhesive 19,
specifically an electrically-conductive adhesive. In the case of
face-up mounting, the lower surface of the light-emitting element
20 is connected to the electrically-conductive members 13 via the
adhesive 19, specifically an electrically-conductive adhesive or an
insulating adhesive.
In the case of a light-emitting element 20, which is not shown,
having a pair of positive and negative electrodes on opposite
surfaces, the light-emitting element 20 is mounted in the depressed
portion 15 of the substrate 10 by bonding the electrode on the
lower surface to an electrically-conductive member 13 via an
electrically-conductive adhesive and connecting the electrode on
the upper surface to another electrically-conductive member 13 with
a wire 18.
Forming Light-Transmissive Member
In the forming of the light-transmissive member 30, the
light-transmissive member 30 is formed in the depressed portion 15
of the substrate 10 to cover the light-emitting element 20.
First, a slurry containing the phosphor 50 and the particles 40
dispersed in the matrix 31 is provided. The slurry is prepared such
that the content of the phosphor 50 falls within the range of 100
parts by mass to 300 parts by mass relative to 100 parts by mass of
the matrix. The slurry is prepared such that the content of the
particles 40 falls within the range of 0.01 parts by mass to less
than 5 parts by mass relative to 100 parts by mass of the matrix.
Particles having an average particle diameter in the range of 1 nm
to 8 nm surface-treated with the surface treatment agent in advance
are used as the particles 40. Instead of the surface-treated
particles 40, the particles 40 coexisting with a dispersing agent
or the surface-treated particles 40 coexisting with a dispersing
agent may be used. The particles 40 coexisting with a dispersing
agent or the surface-treated particles 40 coexisting with a
dispersing agent are, for example, particles that have adsorbed the
dispersing agent obtained by adding the dispersing agent to the
slurry.
Subsequently, the slurry is stirred with a centrifugal stirrer to
disperse the particles 40 in the form of aggregates. The slurry is
charged into the depressed portion 15 to cover the light-emitting
element 20 by an application method such as spraying, screen
printing, and potting (dripping). The slurry is then hardened by
heat, so that the light-transmissive member 30 is formed in the
depressed portion 15 to provide the light-emitting device 100.
Although depending on the material for the matrix 31, the heat is
applied preferably to a temperature of 100.degree. C. to
300.degree. C.
By the above method for manufacturing the light-emitting device
100, the light-emitting device 100 in which the average particle
diameter of the aggregates 41 in the light-transmissive member 30
is about one-tenth of the wavelength of the primary light emitted
from the light-emitting element 20, specifically in the range of 10
nm to 80 nm, is manufactured. Accordingly, the amount of scattered
primary light is improved by Rayleigh scattering from the
aggregates 41, so that the light-emitting device 100 that shows
improved light extraction efficiency is manufactured.
EXAMPLES
The following describes examples and comparative examples according
to the present invention in detail. Needless to say, the present
invention is not limited to the following examples only.
Example 1
A light-emitting device in Example 1 is a top-view SMD LED having
the structure of the illustrative light-emitting device 100 shown
in FIG. 1 and FIG. 2.
The substrate 10 is a package having a rectangular-cuboid shape
measuring 3.0 mm in height, 3.0 mm in width, and 0.52 mm in
thickness. The package is produced by forming the formed body 14 on
a pair of positive and negative (first and second)
electrically-conductive members 13 in an integrated manner. The
substrate 10 is produced by disposing a processed metal plate (lead
frame) including a plurality of pairs of electrically-conductive
members 13 connected to each other in the longitudinal and lateral
directions via suspension leads in a mold, injecting and hardening
liquid components of the formed body 14, releasing the product, and
cutting (separating) the product. In the present example, the
substrate 10 is cut after forming the light-transmissive member 30
encapsulating the light-emitting element 20.
Each of the first and second electrically-conductive members 13 is
a plate-shaped copper-alloy piece having a maximum thickness of 0.2
mm plated with silver. Exposed regions of the lower surfaces of the
first and second electrically-conductive members 13 are
substantially flush with the lower surface of the formed body 14
and constitute the lower surface of the substrate 10. Although not
shown in the drawings, portions (suspension lead portions that have
been cut) of each of the first and second electrically-conductive
members 13 are exposed on lateral end surfaces of the substrate 10.
On the exposed portions, depressions that function as castellations
are formed.
The formed body 14 has a square outer shape measuring 3.0 mm in
height and 3.0 mm in width in a top view, has a maximum thickness
of 0.52 mm, and is made of epoxy resin mixed with titanium oxide.
The depressed portion 15 having a circular shape in a top view
measuring 2.48 mm in diameter and 0.32 mm in depth is formed at a
substantial center of the upper surface of the formed body 14, that
is, the upper surface of the substrate 10. The inclination angle of
the lateral walls of the depressed portion 15 is 95.degree. from
the bottom surface of the depressed portion.
The upper surfaces of the first and second electrically-conductive
members 13 constitute part of the bottom surface of the depressed
portion. One light-emitting element 20 is bonded to the upper
surface of the first electrically-conductive member 13 with a
silicone resin adhesive 19. The light-emitting element 20 is an LED
element that includes a nitride-semiconductor element structure
layered on a sapphire substrate, can emit blue (with a center
wavelength of about 460 nm) light, and measures 650 .mu.m in
height, 650 .mu.m in width, and 120 .mu.m in thickness. One of p-
and n-electrodes of the light-emitting element 20 is connected to
the upper surface of the first electrically-conductive member 13
with a wire 18, and the other one of the p- and n-electrodes is
connected to the upper surface of the second
electrically-conductive member 13 with a wire 18. The wires 18 are
gold wires having a diameter of 25 .mu.m.
A slurry was dripped from a dispenser into the depressed portion 15
of the substrate 10. The slurry was hardened by heat, so that the
light-transmissive member 30 was formed to cover the light-emitting
element 20 to provide the light-emitting device 100.
The slurry contained a silicone resin matrix 31, BAM:Mn phosphor
51, KSF:Mn phosphor 52, and zirconia nanoparticles.
The contained BAM:Mn phosphor 51 had an average particle diameter
of 16.2 .mu.m, and its content was 179.8 parts by mass relative to
100 parts by mass of the matrix 31. The contained KSF:Mn phosphor
52 had an average particle diameter of 26.4 .mu.m, and its content
was 15.6 parts by mass relative to 100 parts by mass of the matrix
31.
The contained zirconia nanoparticles were zirconium oxide particles
having an average particle diameter of 5 nm surface-treated with a
siloxane compound, and its content was 0.1 parts by mass relative
to 100 parts by mass of the matrix 31.
Example 2
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that the content of the zirconia
nanoparticles having an average particle diameter of 5 nm was
changed to 0.5 parts by mass.
Example 3
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that the content of the zirconia
nanoparticles added having an average particle diameter of 5 nm was
changed to 1 part by mass.
Comparative Example 1
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that the content of the zirconia
nanoparticles having an average particle diameter of 5 nm was
changed to 5 parts by mass.
Comparative Example 2
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that the content of the zirconia
nanoparticles having an average particle diameter of 5 nm was
changed to 10 parts by mass.
Comparative Example 3
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that 0.1 parts by mass of zirconia
nanoparticles having an average particle diameter of 10 nm was
contained.
Comparative Example 4
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that 1 part by mass of zirconia
nanoparticles having an average particle diameter of 10 nm was
contained.
Comparative Example 5
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that 10 parts by mass of zirconia
nanoparticles having an average particle diameter of 10 nm was
contained.
Comparative Example 6
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that 0.1 parts by mass of zirconia
nanoparticles having an average particle diameter of 40 nm was
contained.
Comparative Example 7
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that 1 part by mass of zirconia
nanoparticles having an average particle diameter of 40 nm was
contained.
Comparative Example 8
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that 10 parts by mass of zirconia
nanoparticles having an average particle diameter of 40 nm was
contained.
Comparative Example 9
A light-emitting device 100 was produced in substantially the same
manner as Example 1 except that no zirconia nanoparticles were
contained.
Luminous fluxes of the light-emitting devices 100 produced were
measured with an integrating sphere. Table 1 shows the results in
terms of luminous flux ratios. A luminous flux ratio is a ratio of
the luminous flux value in each example to the luminous flux value,
which is regarded as 100, in Comparative Example 9. FIG. 4 shows
the relation between the luminous flux ratios of the light-emitting
devices 100 and the average particle diameter and content of
zirconia nanoparticles.
TABLE-US-00001 TABLE 1 Particles Average particle Content Luminous
flux Sample No. diameter (nm) (part by mass) ratio (%) Example 1 5
0.1 100.8 2 5 0.5 100.8 3 5 1 100.7 Comparative 1 5 5 99.2 example
2 5 10 99.8 3 10 0.1 99.9 4 10 1 98.1 5 10 10 94.1 6 40 0.1 99.6 7
40 1 99.4 8 40 10 95.2 9 -- -- 100 (Note) The symbol "--" in the
table indicates that particles are not contained.
As shown in Table 1 and FIG. 4, since the average particle
diameters and contents of the zirconia nanoparticles in the
light-emitting devices 100 in Examples 1 to 3 met the requirements
of the present invention, the zirconia nanoparticles aggregated to
form aggregates 41 having an average particle diameter of about
one-tenth of the wavelength of blue light emitted from the
light-emitting element 20. Consequently, the effects of Rayleigh
scattering from the aggregates 41 were enhanced, and the luminous
flux ratio, that is, the light extraction efficiency, was
improved.
On the other hand, since the contents of the zirconia nanoparticles
were large in the light-emitting devices 100 in Comparative
Examples 1 and 2, the zirconia nanoparticles aggregated to form
aggregates 41 having an average particle diameter larger than a
quarter of the wavelength of blue light. Consequently, the effects
of Rayleigh scattering from the aggregates 41 were lessened, and
the luminous flux ratio, that is, the light extraction efficiency,
decreased.
Since the average particle diameters of the zirconia nanoparticles
were large in the light-emitting devices 100 in Comparative
Examples 3, 4, 6, and 7, the zirconia nanoparticles aggregated to
form aggregates 41 having an average particle diameter larger than
a quarter of the wavelength of blue light. Consequently, the
effects of Rayleigh scattering from the aggregates 41 were
lessened, and the luminous flux ratio, that is, the light
extraction efficiency, decreased.
Since the average particle diameters and contents of the zirconia
nanoparticles were large in the light-emitting devices 100 in
Comparative Examples 5 and 8, the zirconia nanoparticles aggregated
to form aggregates 41 having an average particle diameter larger
than a quarter of the wavelength of blue light. Consequently, the
effects of Rayleigh scattering from the aggregates 41 were
lessened, and the luminous flux ratio, that is, the light
extraction efficiency, decreased.
Since the light-emitting device 100 in Comparative Example 9 did
not contain zirconia nanoparticles, Rayleigh scattering from
zirconia nanoparticles is not caused. Accordingly, the luminous
flux ratio, that is, the light extraction efficiency decreased
compared with Examples 1 to 3.
INDUSTRIAL APPLICABILITY
The light-emitting devices according to the present disclosure can
be used for light sources for backlights of liquid-crystal
displays, a variety of lighting apparatuses, large format displays,
and various displays for advertisements or destination guide, as
well as digital video cameras, image scanners in apparatuses such
as facsimile machines, copying machines, and scanners, projectors,
and other apparatuses.
* * * * *